Wednesday, 12 February 2014

Tempers ran hot over tarsiers

Philippine tarsier (Tarsius syrichta)Jasper Greek Golangco

A recent post dealt with controversy over the evolution of placentals. This is nothing new. In 1897 debate ranged in the pages of Science about whether tarsiers belonged with lemuroid or anthropoid primates. It was sparked by the work of Hubrecht, who claimed that the embryological development of tarsiers resembled that of higher primates. He pointed to the precocious development of the extraembryonic mesoderm as well as the absence of an allantoic sac and its replacement by the connecting stalk.

Skull of Anaptomorphous

Had he stopped there all might have gone well. But Hubrecht proceeded to give a new interpretation of the primate fossil record, in particular Anaptomorphous homunculus(now placed in Omomyidae). This raised the ire of Charles Earle, curator of fossils at the American Museum of Natural History. He argued on the basis of osteological characters and dentition that tarsiers might represent an intermediate stage between lemuroids and anthropoids but certainly did not belong with the latter (here). In a spirited reply (here), Hubrecht wrote, "It is, indeed, rather hard upon me...to be now pilloried by Mr. Earle as if I had been making that coarse and indiscriminate use of placentary characters in classification against which I have been all the time loudly protesting."

In the next exchange (here), Earle argued for the superiority of palaeontological over embryological methods in determining phylogeny. He rather spoiled the effect by presaging one argument, "On this side of the Atlantic..."

As a footnote it is worth observing that there remain huge gaps in the fossil record of primates and the position of Anaptomorphous is still open to alternative interpretations. Meanwhile Hubrecht's view has triumphed over Earle's with primates split in Strepsirrhini (the lemuroids) and Haplorrhini (tarsiers and anthropoid primates).